I. Field
The present disclosure relates generally to communication, and more specifically to techniques for selecting transmit formats in a wireless communication system.
II. Background
In a wireless communication system, a transmitter typically processes (e.g., encodes, modulates, and channelizes) traffic data in accordance with a transmit format selected for use and generates output chips. A transmit format may also be referred to as a rate, a modulation coding scheme (MCS), a packet format, a transport format, a transmission mode, and so on. A transmit format may indicate various parameters to use for transmission such as a coding scheme, a code rate, a modulation scheme, a data block size, a number of code channels or subcarriers, and so on. The transmitter then processes the output chips to generate a modulated signal and transmits this signal via a wireless channel. The wireless channel distorts the transmitted signal with a channel response and further degrades the signal with noise and interference.
A receiver receives the transmitted signal and processes the received signal to obtain samples. The receiver then processes (e.g., dechannelizes, demodulates, and decodes) the samples in accordance with the selected transmit format to obtain decoded data. The receiver may estimate the received signal quality, e.g., based on a pilot sent by the transmitter. The transmitter and/or receiver may select an appropriate transmit format to use for an upcoming time interval based on the received signal quality.
Transmit format selection refers to the selection of an appropriate transmit format to use for transmission based on channel conditions and other relevant factors. Transmit format selection has a large impact on system performance and is challenging for a time-varying system. Transmit format selection is even more challenging in a multiple-input multiple-output (MIMO) system that employs multiple transmit antennas for data transmission to multiple receive antennas. The transmissions from the multiple transmit antennas interfere with one another, thereby making it more difficult to accurately estimate the received signal quality and select suitable transmit formats for use.
There is therefore a need in the art for techniques to effectively select transmit formats in a MIMO system.